The stator of a dynamoelectric machine such as an electric motor or generator typically includes a core of magnetic material having an axially extending bore for receiving a rotor. The core typically is formed from a plurality of identical laminations which are aligned and arranged in a stack held together by clips. Each lamination includes a plurality of teeth which extend radially into the bore. Slots between each of the teeth extend radially outwardly from the bore. The ends of the teeth and the open ends of the slots define the periphery of the bore.
A plurality of coils formed from insulated conductive wire are inserted into selected core slots with portions of the coils at the ends of the core forming end turn regions. The coils are interconnected to form coil groups or poles. The conductive wires which form the coils, sometimes referred to as stator windings, typically are coated with a varnish or an enamel so that a tough protective coating is formed around each wire. The coating is required so that each wire is well insulated from the other wires. Improvements to or reduction of damage to such coating facilitates improved motor performance by, for example, reducing field failures.
To insert the coils into the stator core slots, it is known to form coil groups with coil forms, locate the coil groups on coil insertion (or injection) tooling, and then move the coil groups from the coil insertion tooling to a stator with portions thereof located in stator slots. Coil injection apparatus for inserting the coils into the stator slots is described, for example, in U.S. Pat. No. 3,949,464. Known tooling for such apparatus typically include a base having a plurality of radially arranged and spaced blades extending from an upper surface of the base. The blades are arranged in a circular array.
With known apparatus, a "stripper" having fins is placed within the bore defined by the circular array of blades. The stripper fins are aligned with and extend into the gaps between adjacent blades. One stripper fin extends into each such gap. The stripper includes an upper, or operative, surface configured to contact segments of the coils which lie within the gaps between adjacent blades and extend into the interior, or bore, established by the circular array of blades. A lower surface of the stripper is connected to an axially movable ram, or pusher rod, which extends through the apparatus base and moves the stripper axially along the bore of the circular array of blades. The stripper typically is constructed of a material such as brass.
A single speed motor typically includes coil groups which establish at least one main winding and an auxiliary or start winding. The coil groups are formed with a winding machine and located on the tooling of coil insertion tooling so that the coil groups are located in gaps between the blades at a location between the stripper and the free ends of the blades. Portions of each coil extend through gaps between the blades and segments of each coil span an interior region of the bore established by the circular array of blades. A stator core is then aligned with and placed on the tooling of the coil injection apparatus or device so that at the open end of the circular array of blades, each blade registers with a stator tooth and so that gaps between adjacent blades register with stator slot openings. The pusher rod then moves the stripper within the circular array of blades and from a retracted position toward the stator core. The fins of the stripper contact the portions of the coils which lie in the gaps between adjacent blades. Also, the surface of the stripper facing the core contacts the segments of the coils which span along the interior of the circular array of blades. Once the stripper contacts the coLls as described above, and as the stripper moves toward the stator core, the stripper forces the coils to move along the blades toward the stator core.
As the stripper begins to move through the bore of the stator core, each fin of the stripper which contacts a coil portion in the blade gaps forces such coil portion into respective aligned stator slots. When the upper surface of the stripper has fully moved through the stator bore, each such coil portion is fully injected into the stator core slots. The stripper is then retracted to a retracted position and the "injected" stator core is removed from the insertion device.
When injecting two coil groups, e.g., main and auxiliary (or start) coil groups, into a stator core, at least a portion of at least the lowermost coil group on the blades directly contacts the fins of the stripper. Typically, some portions of the uppermost coil group also are in direct contact with some of the fins. During the injection process, the stripper fins exert sufficient forces against such coil portions to move the coils axially along the blades and to inject side turn portions thereof into the stator slots. Such forces generally have a sufficient magnitude to not only move the coils along the blades and into the stator slots, but also are sufficient to cause stretching and abrading of the magnet wire which forms the coils.
Such deformations sometimes are referred to as pressure marks. Pressure marks are particularly troublesome because over time, as the wire insulation wears, the insulation may fail and conductor material may be exposed. Such exposure may lead to a field failure of the motor. Also, if the magnetic wire is sufficiently deformed or stretched, there may be reduced operational efficiency for the motor due, for example, to increased resistance of the magnet wire and possibly even short circuiting of the wire.
With respect to known strippers, such strippers generally are constructed from a soft metal such as brass in an attempt to limit the damage to insulation and pressure marks on the coils caused during the coil injection process. Manufacturing brass strippers is, of course, expensive in terms of both the material and labor. In addition, the brass fins of the stripper usually must be polished at regular intervals to remove nicks and prevent sharp insulation piercing edges from forming. Polishing such strippers, of course, is time consuming and expensive. Further, the fins of a stripper are susceptible to damage if, for example, the stripper is dropped. If a stripper is dropped, a fin may chip or even break-off. Such a damaged stripper may have to be discarded.
In addition, with known strippers, as the number of windings forming the coil groups being injected increases, the likelihood of coil binding, or "lock-up", also increases. Also, the windings which form the coils may be twisted during the injection process or may get caught between the stripper and one or more of the circular array of blades. When this occurs, the stripper may become locked and axial movement of the stripper may be prevented. Usually, the chance of lock-up is reduced by limiting the number of coils injected in one-pass of the stripper through the rotor bore. Thus, the likelihood of occurrence of a lock-up condition with known strippers can be reduced with this technique.
When using the stripper and one-pass process described above to inject three or more coil groups into a stator core, the forces exerted by the stripper against the coil wires are very high. As a result, the coil wires may be significantly damaged. In addition, although it is highly desirable in some motor applications, e.g., when the effect of inductive reactance is significant, to have the start winding coil group as close as possible to the stator bore to facilitate magnetic coupling between the fields generated by the start winding and rotor, the start winding coil wire and insulation usually cannot withstand the direct high forces which must be exerted against the start winding by the stripper fins in such one-pass injection process. The start winding wire and insulation, for example, usually is much thinner than the main winding wire and insulation. The start coils, therefore, preferable would be located on an injection device so that the fins of the stripper do not directly contact such coils, i.e., the stripper proximate coils which are in direct contact with the fins of the stripper preferably would be main winding coils. As a result, the start winding coils usually are, after placement in the stator core slots, either located at a distance remote from the bore, i.e., at the closed slot ends, or at an intermediate slot location between two main windings.
To avoid the formation of excessive pressure marks and reduce the possibility of a lock-up condition when injecting three or more coil groups into a stator core, a two-pass injection process typically is utilized. For example, a first main coil group and an auxiliary coil group are injected into the stator core in a first pass. A second main coil group is then injected into the stator core in a second pass. Such a two-pass coil injection process enables use of lower forces as compared to the magnitude of forces required for a one-pass injection of three coil groups using known strippers. Even though lower forces are used in the two-pass injection process, such lower forces are still sufficient to create pressure marks on the coil wires. Of course, even higher forces would have to be used to inject three coil groups in one pass, and such higher forces inevitably seem to cause unacceptable damage to the coil wires.
Although a two-pass process is effective for reducing damage to the coil wires, such two-pass process is more labor intensive and time consuming than known one-pass processes used for single speed motors. By reducing the labor and time required for injecting more than two coil groups into stator cores, manufacturing costs for such stators could be reduced.
Known attempts have been made to perform one-pass coil injection of three or more coil groups with complex shaped strippers. The forces necessary to inject the coils using known complex shaped strippers, however, are believed to be high which, as explained above, can result in the stripper fins forming pressure marks on the coil wires. Also, complex shaped strippers are believed to be expensive to manufacture and maintain.
Another known attempt at such one-pass injection has utilized a structure in which two brass strippers were stacked, one on top of the other, within the circular array of blades. A post separated the strippers. The lowermost stripper utilized a 4-leg star which, as described hereinafter, separated the main coil group and the start coil group to reduce the forces which the start coil wires exerted against the main coil wires during the injection process. However, with this approach, it is believed that the forces necessary to inject the coils with such a structure would be objectionably high. Also, two brass strippers must be manufactured and maintained. As explained above, the manufacture and maintenance of such brass strippers is expensive.
When using a two stripper device, the start and main winding coil groups are first loaded over the pre-positioned lowermost stripper. The upper stripper is then inserted within the bore of the circular array of blades, with the stripper fins extending into gaps between adjacent blades, and lowered to rest on the upwardly extending post of the lowermost stripper. The turns of the second main coil group are then loaded into the blade gaps above the fins of the upper stripper.
Although it is desirable to fully automate the coil injection process, known automation equipment cannot consistently operate within the small dimensional tolerances required for aligning stripper fins with gaps between adjacent blades. Therefore, when using a two stripper process, a human operator must perform the task of aligning the upper stripper so that each stripper fin extends into a gap between adjacent blades and initially placing the upper stripper into the tooling. Any such human performed functions, of course, inevitably increase process costs and decrease process speed.
Accordingly, it would be desirable and advantageous to provide a equipment for placing, in one-pass, coils on a stator core of a multi-speed motor, and to provide a stripper that exerts, against the coil wires, forces less than the forces exerted by known strippers. It would also be desirable and advantageous to provide such a stripper which is low in cost, both for manufacture and maintenance, and which eliminates a need for a human operator to orient the stripper within the circular array of blades of the injection device during the manufacturing process.
An object of the present invention is to provide a stripper for placing, in one-pass, winding coils on a stator for a multiple speed motor.
Another object of the present invention is to provide a stripper which is low cost and does not have any significant maintenance requirements or costs.
Still another object of the invention is to provide a stripper which injects the winding coils into a stator core for a multi-speed motor by exerting significantly lower forces against the coil wires as compared to the forces exerted against the coil wires by known strippers.
Yet another object of the present invention is to provide an improved stripper and process which facilitates full automation of magnet wire coil injection processes.